# A Practical Manual of the Compass: A Short Treatise on the Errors of the Magnetic Compass, with the Methods Employed in the U.S. Navy for Compensating for Deviations, and a Description of Service Instruments, Including the Gyro-compass

United States Naval Institute, 1916 - Compass - 146 pages

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Page 17 - The name magnet, or lodestone, was given by the ancients to certain hard, black stones which possessed the property of attracting to them small pieces of iron or steel. 25. Artificial Magnets. — If a piece of iron, or better still a piece of hard steel, be rubbed with a lodestone, it will be found to have also acquired the properties characteristic of the magnet ; it will attract light bits of iron, and, if hung up by a thread, it will point north and south. 26. First Laws of Magnets. — If two...
Page 32 - The heeling error is corrected by a permanent magnet placed in a vertical position directly under the center of the compass. Such a magnet has no effect upon the compass when the ship is upright ; but since its force acts in an opposite direction to the force of the ship which causes heeling error, is equal to the latter in amount, and is exerted under the same conditions, it affords an effective compensation. For similar reasons to those affecting the compensation of B and C, the correction by means...
Page 34 - This form is adapted to a computation from observations on 24 equidistant compass headings. It may be used for 12 or 8 equidistant observations by omitting the intermediate headings, but the divisors for finding A, B, and C must be 3 or 2, respectively, and those for finding D and E must be } or I, respectively.
Page 10 - Having once satisfied himself that the general rule holds, the navigator may save the necessity of reasoning out in each case the direction in which the error must be applied, and need only charge his mind with some single formula which will cover all cases. Such a one is "the following: When the CORRECT direction is to the RIGHT, the error is EAST. The words correct-riaht-east, in such a case, would be the key to all of his solutions.
Page 28 - ... south pole in the starboard angle, the semicircular forces will be represented by two magnets, one fore-and-aft and the other athwartship, and compensation may be made by two separate magnets lying respectively in the directions stated, but with their north or repelling poles in the position occupied by the south or attracting poles of the ship's force. Figure 17 represents the conditions that have been described. If 0 be the center of the compass, XX...
Page 14 - The line may in fact be considered as the margin of a compass card cut at the North point and straightened. The vertical line is intersected at each of the 32 points by two straight lines, inclined to it at angles of 60°.
Page 12 - ... represent magnetic directions, but by assuming that they do we obtain a series of fictitious deviations, the mean value of which is the error common to all. Upon deducting this error from each of the fictitious deviations, we obtain the correct values. If ship and shore observers are provided with watches which have been compared with one another, the times may be noted at each observation, and thus afford a means of locating errors due to misunderstanding of signals.
Page 127 - By so doing we have steamed directly from a place at which the rate of tilting of xx was 37° in 12 hours to a point at which the rate is 108° in 12 hours. Suppose in starting from B, we had steamed 20 knots per hour instead of 10 knots. We would thus arrive at C in onehalf the time it would have taken us at 10 knots and the rate at which this change in the tilt of xx takes place, as due to differences in speed, would be twice as great in the second case as in the first case. Thus speed is introduced...
Page 17 - Introductory. — These notes are not a complete treatise on the deviation of the compass, but are an attempt to explain, by simple laws of magnets, how deviation is produced by the iron of a ship, and, by the same laws, how the deviation may be corrected. It is an explanation of principles involved, based upon the physical laws of the attraction and repulsion of magnets.
Page 86 - Com reports in accordance with the instructions laid down in the prescribed forms or issued from time to time. (2) When the ship is under way and the weather permits, he shall each day ascertain by observation the error of the standard compass and report the result in writing to the captain.